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Least number x such that number of primes between sigma(x) and x equals n.
1

%I #15 Mar 01 2020 07:17:57

%S 2,4,10,12,16,46,28,24,44,30,42,40,36,54,48,66,178,78,104,80,102,60,

%T 128,72,84,152,90,138,255,96,108,174,140,126,132,266,160,150,248,222,

%U 156,120,246,200,144,198,634,224,220,204,370,260,168,376,555,430,354,308

%N Least number x such that number of primes between sigma(x) and x equals n.

%H Amiram Eldar, <a href="/A085344/b085344.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = Min{x; A085341(x)=n}.

%t m = 100; seq = Table[0, {m}]; c = 0; n = 0; While[c < m, n++; i = PrimePi[ DivisorSigma[1, n]] - PrimePi[n]; If[i <= m && seq[[i]] == 0, c++; seq[[i]] = n]]; seq (* _Amiram Eldar_, Mar 01 2020 *)

%o (PARI) a(n) = {my(x=1); while (primepi(sigma(x)) - primepi(x) != n, x++); x;} \\ _Michel Marcus_, Mar 01 2020

%Y Cf. A000720, A000010, A000203, A070803, A070804.

%Y Cf. A085341, A085342, A085343, A085345, A085346, A085347.

%K nonn

%O 1,1

%A _Labos Elemer_, Jul 10 2003